1. Field of the Invention
The invention relates to a three (or more) component additive combination for distillate fuel oils, comprising (A) an ethylene backbone distillate fuel oil pour depressant polymer, (B) a second polymer having alkyl side chains of 6 to 30 carbon atoms defined by carboxylic acid ester or olefin moieties, and (C) a nitrogen compound e.g. amides and salts of a carboxylic acid or anhydride. This combination is particularly useful in distillate fuel oils for controlling the size of wax crystals that form at low temperatures, and for inhibiting agglomeration of the crystals.
2. Description of the Prior Art
Two component additive systems for treating distillate fuel oil to limit the size of wax crystals that form in the fuel oil in cold weather are known, as shown by the following patents.
United Kingdom Pat. No. 1,469,016 teaches ethylene polymer or copolymer, which is a pour depressant for middle distillate fuel, in combination with a second polymer having alkyl groups of 6 to 18 carbon atoms, which is a polymer of an olefin or unsaturated dicarboxylic acid ester, is useful in improving the cold flow properties of middle distillate fuel oils.
U.S. Pat. No. 3,982,909 teaches nitrogen compounds such as amides, diamides, and ammonium salts of: monoamides or monoesters of dicarboxylic acids, alone or in combination with a hydrocarbon microcrystalline wax and/or a pour point depressant, particularly an ethylene backbone polymeric pour point depressant, are wax crystal modifiers and cold flow improvers for middle distillate fuel oils, particularly diesel fuel.
U.S. Pat. Nos. 3,444,082 and 3,846,093 teach various amides and salts of alkenyl succinic anhydride reacted with amines, in combination with ethylene copolymer pour point depressants, for distillate fuels.